Deep‐UV exciton emission from Mg1 − xCaxO—A first‐principle investigation

Abstract

AbstractIn order to investigate the ultraviolet and electron emission properties of rock‐salt Mg1 − xCaxO, first‐principle calculations are carried out with x ranging from 0 to 0.5. The electron–hole interaction is taken into account by solving the Bethe–Salpeter equation. In pure MgO, the calculated exciton binding‐energy value of 83 ± 3 meV is quite close to the published experimental values. The electronic properties of doped MgO are investigated based on the super‐cell model. Both the optical bandgap and the exciton binding energy of the super cell of Mg1 − xCaxO are calculated for five discrete compositions, with an increasing amount x of CaO. The results show that there are strong excitonic effects in all of these materials. A rapid reduction in bandgap value is observed for Mg1 − xCaxO, when increasing the x value. The exciton binding energy of Mg1 − xCaxO shows a minimum value of about 40 meV around x = 0.2. In all of these cases, the exciton is stable at room temperature. The lowest excitation levels in Mg1 − xCaxO are determined by dark excitons. The occurrence of these dark excitons might explain why Mg1 − xCaxO is a strong source of delayed electron emission, after being bombarded by ions in a plasma.